I design and recolor with Inkscape. Occasionnaly, if the source file is in a bitmap format (BMP/JPG/GIF), I'll use MS Paint but I prefer working on a vector file. So I'll either use the vectorizing feature of Inkscape or retrace the model.

On the one and only model that I recolored so far, I used MS Paint. I do now have Photoshop CS4 that I got a couple of weeks ago, but haven't tried to use it for anything as I am still learning about it.

Chris, my wife has an iPad and I checked in the app store and saw only one app that may work in repainting, but it was advertised as actually painting a picture from a blank canvas. Couldn't figure out if something could be imported and worked on by description.....didn't want to buy only to find it would not do what expected for repainting. There is a Photoshop app, but it appears that it is tailored to actually do basic photo editing like adjust color, brightness, contrast and cropping.

Another thing that has me thinking, I am not too familiar with how Apple syncs stuff when a master document is maintained on a desktop while edits are done on the iPad. Makes me wonder if the syncing will delete one or the other document. I'm pretty much only familiar with syncing music, movies and photos that are already edited and won't be synced anymore. Something to research I suppose.